Designing and operating a garden compost heap

ARGUABLY, the most important decision about operating a compost heap – besides the decision to actually set one up – is where to locate it.

A garden compost heap can deliver a steady flow of nutritious soil improver, but it is going to be almost next to useless if it’s near impossible to access.

Impossible to access and perhaps also impossible to get at with a garden fork, to introduce oxygen to the rotting-down process.

Oxygen is one of the key ingredients of a properly-functioning compost heap. Cooked food, meat, dairy products or fat are most definitely not – not only because of the way they might break down but because of the risk of attracting vermin.

Nor do you want to be adding diseased plants or perennial (coming back every year) weeds, for fear of transferring the disease or weeds back into the soil when adding the compost to it.

Water is another key ingredient, but any garden compost is most likely to primarily comprise grass cuttings, vegetable peelings, even egg shells and newspapers. As the renowned gardener-broadcaster, Monty Don, describes: the newspapers provide the ‘brown’ to mix with the ‘green’ of the grass cuttings and leaves.

The ‘brown’ of carbon; the ‘green’ of nitrogen.

On the BBC TV programme he presents, Gardeners’ World, his compost heap is a multi-bay affair.

His garden is quite big, so he has the space to make his compost bays to the dimensions of builders’ merchant pallets, as described in this short video:

His first bay is what he describes as an ‘assembly point’, where the starter material is first gathered. Let’s call that Bay One. The material is then shredded into tinier pieces, and placed into Bay Two, where the composting truly begins.

Try not to let a compost heap dry out, since moist conditions encourage the bacteria, fungi, nematodes, worms, beetles, slugs and other organisms munching their way through the heap – insodoing generating heat.

To add much-needed oxygen, by turning the heap, Monty has the benefit of a third bay, into which the contents of Bay Two are tipped. 

It could as easily be tipping from one (usually plastic) bin to another. It’s okay to place the bays / bins directly onto soil, for the various organisms to find their way into the heap, unimpeded.

No fresh material should be added to the heap at this point. And, after around four months (during which time the heap might have been turned three or four times), there is probably a perfectly good mulch, available for use in the garden.

A fourth or even a fifth bay (intermediate ones being used for turning) is where the finished compost is kept, ready and waiting to be spread.

Monty Don’s test of ‘finished compost’ is its feel (“nice” to handle) and its smell (“good”).

Don notes that no two compost heaps will be the same. Meanwhile, gardening legend, the now late Geoffrey Hamilton, writes (in his Gardeners’ World Practical Gardening Course): “The nutrient value of garden compost is very variable, but you can be sure it contains a full complement of trace elements.”

So, if beginning with a relatively bare plot of land, think ‘compost heap’ relatively early on, at the planning stage. Locating one’s compost bays or bins in a relatively sunny spot can also have a beneficial effect on the composting process.

Further reading:

Gardeners’ World Practical Gardening Course, by Geoffrey Hamilton, here:

Mike Wilson is a member of the Place Design Scotland team